It is well known in the electrographic art to use magnetic brush development apparatus for applying marking particles to latent images on a photoconductor or other image member that is advanced past the magnetic brush. Developer material, comprised of magnetic carrier particles and marking particles, may initially be mixed in a sump to triboelectrically charge the material prior to delivering it to a developer roller of the magnetic brush apparatus. It is also known to meter the flow of developer material to the magnetic brush and to gate, or shut off, the flow of material to the brush under certain circumstances. Metering of the developer material can be accomplished by a skive or by feeding the material through a slot leading to the magnetic brush. Gating of the developer material may be achieved by isolating the slot from the magnetic brush.
Such a slot-feeding apparatus is disclosed in commonly assigned U.S. Pat. No. 4,956,674, issued on Sep. 11, 1990 in the name of Kalyandurg. This apparatus has a rotary feed mechanism which delivers developer material from a sump to a magnetic brush. A gating device between the sump and the magnetic brush rotates about an axis substantially coaxial with the rotary feed mechanism between (1) an open position communicating the magnetic brush and the sump and (2) a closed position substantially isolating the magnetic brush from the sump. The gating device is drivingly connected to a solenoid by a linking mechanism. While such a method of connecting the solenoid to the gating device operates well for its intended purpose, it does involve a number of moving parts. Over time, these part will wear, making it more difficult to accurately position the gating device. A mechanism is desired which will accurately position the gating device over an extended period of time.
In the Kalyandurg apparatus, the rotation of the gating device from the closed to the open position is opposed to the flow of developer material within the gating device. When the solenoid is energized to rotate the gating device to its open position, the solenoid will have to overcome the resistance caused by the flow of developer material within the gating device. An apparatus wherein rotation of the gating device from a closed to an open position is in the direction of developer material flow would decrease the time and energy it takes to rotate the metering device from the closed position to the open position.
A lower slot in the Kalyandurg gating device occupies only about 25.degree. of the circumference of the gating device. When the gating device is in the closed position, a certain amount of developer material will be trapped in the gating device. An arrangement allowing most of the developer material to flow back into the sump for continuous mixing would be more desirable.